[PATCH v2 1/8] KVM: arm64: nv: Disallow KVM_CAP_ARM_MTE + FEAT_EL2

[Oliver Upton <oupton@kernel.org>]

KVM's nested implementation already hides FEAT_MTE and its laundry list
of derivatives from an NV guest. While good, this is insonsistent with
the UAPI which does not explicitly prevent the combination of MTE and
NV.

Bite the bullet and refuse to create a nested VM if KVM_CAP_ARM_MTE has
been enabled.

Cc: stable@vger.kernel.org
Fixes: a7484c80e5ca ("KVM: arm64: Allow userspace to request KVM_ARM_VCPU_EL2*")
Signed-off-by: Oliver Upton <oupton@kernel.org>
---
 Documentation/virt/kvm/api.rst |  1 +
 arch/arm64/kvm/arm.c           | 16 +++++++++++-----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index e95c9cda085d..4ce4166d415f 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -3602,6 +3602,7 @@ Possible features:
 	- KVM_ARM_VCPU_HAS_EL2: Enable Nested Virtualisation support,
 	  booting the guest from EL2 instead of EL1.
 	  Depends on KVM_CAP_ARM_EL2.
+          Cannot be enabled if KVM_CAP_ARM_MTE has been enabled for the VM.
 	  The VM is running with HCR_EL2.E2H being RES1 (VHE) unless
 	  KVM_ARM_VCPU_HAS_EL2_E2H0 is also set.
 
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 157bf4b81202..4108ff30830c 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -480,7 +480,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		r = cpus_have_final_cap(ARM64_HAS_32BIT_EL1);
 		break;
 	case KVM_CAP_ARM_EL2:
-		r = cpus_have_final_cap(ARM64_HAS_NESTED_VIRT);
+		/* Nested virt is incompatible with MTE */
+		if (kvm && kvm_has_mte(kvm))
+			r = 0;
+		else
+			r = cpus_have_final_cap(ARM64_HAS_NESTED_VIRT);
 		break;
 	case KVM_CAP_ARM_EL2_E2H0:
 		r = cpus_have_final_cap(ARM64_HAS_HCR_NV1);
@@ -1793,13 +1797,15 @@ static int kvm_vcpu_init_check_features(struct kvm_vcpu *vcpu,
 	    !test_bit(KVM_ARM_VCPU_PMU_V3, &features))
 		return -EINVAL;
 
+	/* MTE is incompatible with AArch32 and nested virt */
+	if (kvm_has_mte(vcpu->kvm) &&
+	    (test_bit(KVM_ARM_VCPU_EL1_32BIT, &features) ||
+	     test_bit(KVM_ARM_VCPU_HAS_EL2, &features)))
+		return -EINVAL;
+
 	if (!test_bit(KVM_ARM_VCPU_EL1_32BIT, &features))
 		return 0;
 
-	/* MTE is incompatible with AArch32 */
-	if (kvm_has_mte(vcpu->kvm))
-		return -EINVAL;
-
 	/* NV is incompatible with AArch32 */
 	if (test_bit(KVM_ARM_VCPU_HAS_EL2, &features))
 		return -EINVAL;
-- 
2.47.3